Method and device achieveing a flow of stock in a forming tank

ABSTRACT

The invention relates to a method and an arrangement for producing a flow of stock in a moulding tank (1). In this, stock is pumped into the moulding tank (1) at the bottom (1a) and allowed to flow up over the brim (1b) thereof. During its rise in the moulding tank (1), the flow of stock pumped in is distributed by at least one grating placed essentially horizontally and provided with flow openings. An arrangement for performing the said method comprises a line (2a, 2b), connected to the moulding tank (1) and a machine vat for ready prepared stock, for delivering fresh stock to the moulding tank (1) by means of a pump (5) connecting with the line (2a, 2b). The line (2b) opens out in an area close to the bottom (1a) of the moulding tank (1) in such a way that an upwardly directed flow of stock is obtained. The pump (5) is adapted to deliver excess stock so that excess stock is allowed to flow over the brim (1b) of the moulding tank (1). At least one essentially horizontal grating (6, 7) provided with flow openings is arranged in the moulding tank (1).

The present invention relates to a method of producing a flow of stockin a moulding tank.

The invention also relates to an arrangement in a moulding tank forproducing a flow of stock therein, comprising a line, connected to themoulding tank and a machine vat for ready prepared stock, for deliveringa fresh stock to the moulding tank by means of a pump which connectswith the line.

Moulding tanks of this type are used to produce a fibre product, forexample an egg carton or some other packaging product, from the fibresin the stock by means of a male tool with permeable walls and with theaid of a vacuum which sucks the water out of the stock so that thefibres remain on the outside of the tool. In order that the thickness ofthe fibre layer on the tool and hence the thickness of the product willbe as uniform as possible it is essential that the fibre concentrationof the flow of stock be as even as possible, at least in the upper areasof the tank.

In a known moulding tank the flow of stock is directed essentiallyhorizontally. Two serious disadvantages arise as a consequence of thisdirection of flow; on the one hand most of the fibres in the fibreproduct become oriented in the direction of flow of the stock, whichgives the product anisotropic characteristics, on the other thethickness of the fibre layer tends to become greatest where the flow ofstock first encounters the tool. Anisotropy in the product means, forexample, that it tends to become warped as the product dries out. Theunderlying reasons for this are well known to the person skilled in theart.

The object of the present invention is to achieve a method of the saidtype which eliminates the above-mentioned disadvantages. This isachieved according to the invention in that stock is pumped into thebottom of the moulding tank and allowed to flow up over its brim andthat the flow of stock pumped in is distributed during its rise in themoulding tank by at least one grating, provided with flow openings andpositioned essentially horizontally.

According to a special characteristic of the method according to theinvention, a simplified handling of the overflow quantity of stock isachieved in that the overflowed stock is collected and together withfresh stock is pumped back into the moulding tank.

An arrangement of the type described in the preamble, by means of whichthe method according to the invention can be performed, is characterisedin that the line opens in an area close to the bottom of the mouldingtank in such a way that an upwardly directed flow of stock is obtained,that the pump is adapted to deliver excess stock so that excess stockcan flow over the brim of the moulding tank and that at least oneessentially horizontal grating, provided with flow openings, is arrangedin the moulding tank.

According to a special characteristic of the invention the arrangementcomprises a collecting tank for the excess stock and the pump is adaptedto pump the excess stock from the collecting tank together with thefresh stock to the moulding tank, thereby achieving especiallyadvantageous flow paths for the stock.

In order to obtain an optimum dispersal of fibres in the stock thearrangement, as will be apparent from another special characteristic ofthe invention, comprises two gratings positioned approximatelysymmetrically in relation to the half-height of the moulding tank, thelower grating having larger through-flow openings than the upper gratingbut the total through-flow area of both gratings being approximatelyequal.

The invention will be further explained below with reference to theenclosed drawing in which

FIG. 1 shows an embodiment of an arrangement according to the inventionin plan view from the side and

FIG. 2 the arrangement in a plan view from above.

In the drawing 1 denotes a moulding tank for stock intended to be usedas described in the preamble. The tank 1 is connected by way of a line2a to a machine vat, not shown in the drawing, for ready prepared stock.In the embodiment shown in the drawing the tank 1 is surrounded by acollecting tank 3. A pump 5, driven by an electric motor 4 and adaptedto pump excess stock to the moulding tank, is connected into the line 2aso that excess stock can flow over the brim of the moulding tank anddown into the collecting tank 3. A line 2b connects the collecting tank3 to the moulding tank by way of the pump 5. The mouth 2b1 of the line2b in the tank is situated in an area close to the bottom 1a of thetank, one side 1c of the said tank being specifically penetrated at apoint situated approximately midway between the edges of this side. Bymeans of this location of the mouth 2b1 an upwardly directed flow ofstock is obtained in the moulding tank 1.

The bottom 1a of the moulding tank is inclined so that the tank can bedrained by way of a line 2c. It is known that fibres tend to flocculate.In order to prevent the occurrence of such flocs two horizontal gratings6, 7 are arranged in the moulding tank 1. The said gratings arepreferably made of perforated plate, the lower grating 7 having a largerhole diameter than the upper grating 6, but the perforation beingexecuted so that the total through-flow areas of the two gratings areessentially equal.

In operation the arrangement according to the invention functions asfollows: Fresh stock is fed into the moulding tank 1 from the machinevat, not shown in the drawing, by way of the line 2a. Fresh stock,together with stock which has flowed over the brim 1b, is pumped bymeans of the pump 5 by way of line 2b to the moulding tank 1,specifically to the bottom 1a thereof. In this way an upwardly directedflow of stock is achieved which is homogenised by the gratings 6, 7.

The fact that the flow is directed upwards is important in achieving afibre layer of even thickness on the male tool described in thepreamble. That is to say the fibres in the upwardly directed flow areoriented in random directions, at least at the instant the fibres reachthe male tool, as a result of which the anisotropy in the productreferred to earlier is virtually zero.

It will be evident to the person skilled in the art that means ofcontrol are required for controlling valves which are not shown ordescribed, so that a suitable flow is obtained with respect to the stocklevel sensed by means of level sensors. It is further obvious that theembodiment of the arrangement according to the invention can be modifiedin many ways within the framework of the invention.

What is claimed is:
 1. A method of producing a flow of stock in amolding tank, comprising:pumping stock into the molding tank at thebottom of the molding tank, the molding tank having a brim, so that aflow of stock flows upwards from the bottom of the tank to the top ofthe tank and over the brim of the tank; and distributing the flow ofstock, as it flows upwards from the bottom of the molding tank, by atleast one grating disposed across the tank essentially horizontally,between the bottom of the molding tank and the brim, the grating havingflow openings to evenly distribute fibers contained in the stock atleast at an upper part of the molding tank.
 2. A method as recited inclaim 1, further comprising collecting stock after overflowing the brimof the tank, and pumping the collected stock back into the tank togetherwith fresh stock.
 3. Apparatus in a molding tank in order to produce aflow of stock therein, comprising:a molding tank having a brim; a line,coupled to the molding tank for delivering fresh stock to the moldingtank, the line opening into the molding tank close to a bottom of themolding tank to produce an upwardly directed flow of stock when stockflows through the line; a pump, connecting with the line, to pump stockin the line into the molding tank, the pump being adapted to deliverexcess stock so that excess stock flows over the brim of the moldingtank; and at least one grating provided with flow openings and disposedessentially horizontally across the molding tank between the lineopening into the molding tank and the brim.
 4. Apparatus as recited inclaim 3, further comprising a collecting tank disposed to receive theexcess stock flowing over the brim of the molding tank, wherein the pumpis adapted to pump the excess stock from the collecting tank togetherwith fresh stock into the molding tank.
 5. Apparatus as recited in claim3, wherein the at least one essentially horizontal grating includesupper and lower gratings, placed approximately parallel and spacedapproximately equidistant from a molding tank mid-height point, thelower grating having larger through-flow openings than the uppergrating, total through-flow areas of the upper and lower gratings beingapproximately equal.
 6. Apparatus as recited in claim 4, wherein the atleast one essentially horizontal grating includes upper and lowergratings, placed approximately parallel and spaced approximatelyequidistant from a molding tank mid-height point, the lower gratinghaving larger through-flow openings than the upper grating, totalthrough-flow areas of the upper and lower gratings being approximatelyequal.